Evaporator defrosting means



March 15, 1960 L. J. MANN ETAL 2,928,258

EVAPORATOR DEFROSTING MEANS Filed March 7, 1957 INVENTOR. Leonard J Mann By John 6. Miller Their Attorney the food storage compartment. partment 26 is a sealed motor-compressor unit 28 pro- United States Patent EVAPORATOR nnrnosrmc mans Leonard J. Mann, Dayton, and John C. Miller, Spring Valley, Ohio, assignors to General Motors Corporation,

This invention relates to refrigerating apparatus and more particularly to means for defrosting the evaporator and simultaneously preventing the flow of liquid in the suction line.

The evaporators of refrigerating apparatus have been defrosted inmany different ways. One of the problems in defrosting is the liability of liquid refrigerant to be forced out of the evaporator into the suction line during the defrost period where it may be drawn into the compressor. The liquid refrigerant is likely to cause damage in the event that it is drawn into the compressor. It has been proposed to provide a separate heater in the suction line for evaporating any liquid refrigerant which may enter therein. This, however, adds sufficiently to the cost of the system that it is not practical for large volume, low cost refrigerators.

It is an object of this invention to provide a defrosting system wherein the heater used to defrost the evaporator is also used to evaporate any liquid refrigerant which may enter the suction line.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawings, wherein a preferred form of the present invention is clearly shown.

In the drawing:

The figure is a diagrammatic representation of a refrigerating system embodying one form of our invention.

Referring now to the drawing, there is illustrated in dot-dash'outline a refrigerator cabinet having an upper freezing compartment 22, a lower food storage compartment 24 and a machinery compartment 26 below In the machinery comvided with a superheat removal coil 30. The compressor pumps compressed refrigerant through the condenser 32 located at the back of the cabinet 20. From the condenser 32 the liquid refrigerant fiows through a capillary tube restrictor 34 which controls the expansion of the liquid refrigerant into the bottom portion 36 of the evaporator 38. The evaporator 38 has its passages extending upwardly in serpentine fashion within the freezing compartment 22. The evaporator 38 normally operates at below freezing temperatures in order to freeze the foodstuffs within the compartment 22 and also to provide refrigeration for the food storage compartment 24. This causes moisture from the atmosphere to deposit in the form of frost upon the evaporator 38. The frost interferes with the efficiency of the evaporator and therefore must be periodically removed. The top portion of the evaporator is connected to a downwardly extending suction line connection 40.

To defrost the evaporator 38 an electric heater 42 is wrapped helically around the bottom portion 36. This heater 42 has one terminal connected to the supply conductor 44. The second terminal of the heater is connected to the defroster clock 46 which may be of the type shown in the Goodhouse et al. Patent 2,711,456, issued June 21, 1955. This clock 46 controls the energization of the heater '42. The heating of the lower por' tion 36 of the evaporator 38 will boil the liquid refrigerant therein causing the bubbles of vapor to pass upwardly through the serpentine refrigerant passage in the evapo' .ator to heat the evaporator sufficiently to melt the frost thereon. There is danger that this bubbling of refrigerant vapor upwardly through the refrigerant passages will carry some liquid refrigerant down into the suction line 40. If this liquid refrigerant enters the compressor in liquid form, there is considerable danger that the compressor will be damaged.

According to my invention, I extend the suction line 40 transversely across the bottom of the freezing compartment to provide a horizontal portion 48 directly beneath the lower portion 36 of the evaporator 38 and in heat transfer relationship with the heater 42. If any liquid refrigerant flows downwardly through and/or collects in the suction line 40 during a defrosting period, it will be heated and completely vaporized in this horizontal portion 48 by the electric heater 42. Any refrigerant flowing from the horizontal portion 48 through the remaining portion 50 of the suction line 40 back to the suction entrance of the compressor 28 will therefore be completely vaporized.

The motor-compressor unit 28 has one terminal connected through the thermostatic switch 52 to the supply conductor 44. The thermostatic switch 52 is controlled in accordance with the temperature of the thermostat bulb 54 located in heat exchange relation with the outlet of the evaporator 38. The second terminal of the sealed motor-compressor unit is connected to the clock-type defroster control 46. This defroster control 46 has one terminal connected to the supply conductor 56. Normally, the defroster control 46 connects the supply conductor 56 with the motor-compressor unit 28. However, periodically, such as once every twenty-four hours, the defroster clock 46 disconnects from the sealed unit 28 and connects to the heater 42 to energize it for a defrosting period. This stops the operation of the compressor unit 28. The defrosting period continues until the thermostat bulb 58 located upon the top of the evaporator 38 in heat transfer relation therewith reaches a predetermined temperature above freezing such as 34 or 36 F. This bulb 58 is connected by a capillary tube 60 with the clock defroster 46 and causes the disconnection of the heater 42 and the reconnection of the compressor unit 28 to terminate the defrosting period and resume refrigeration.

Thus, by this simple arrangement, one heater not only serves to defrost the evaporator but this same section of the heater is used to impart heat to the adjacent horizontal portion of the suction line to prevent liquid refrigerant from collecting or passing through the suction line.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, as may come within the scope of the claims whichfollow.

What is claimed is as follows:

1. Refrigerating apparatus including refrigerant liquefying means and generally vertical sinuously wound Y evaporating means having a horizontal liquid refrigerant lowest pass refrigerant passage portion for insuring that Refea'ences: Cited intthe. file: of this; Qatcnt.

all the liquid passing through said suction cond uit con- UNITED STATES PATENTS nection is in the form of vapor, sald suction line connection extending tosaidliquefying means. 2,601,466 Thomas June 1952 2. The apparatus of claim 1 wherein said suction con- 5 2:608834 Q Y P 2, 1952 (hit connection is below said lowest pass refrigerant 2,688,850 Whlte P 14, 1954 passage porti Hornaday et a1; Sept. 20, 

